When police arrived at the big house by the marsh in North Scituate after midnight Jan. 1, 20 or 30 teens bolted. Others hid. Inside, police spotted two 55-gallon bins full of empty beer, wine, and liquor bottles. Another 50 empties and 10 pizza boxes were scattered all over. They smelled weed. In the basement, an 18-year-old slumped in a chair, too drunk to move.

Then the homeowner appeared, smelling of alcohol and unsteady on her feet, police said. She explained that she had gone up to her room before midnight. She seemed unaware a boy was unconscious in her home.

We have a law for this kind of thing, a statute driven by completely preventable tragedies: the drunk 16-year-old who punched a window before he left a party, then collapsed and bled to death on a freezing stoop; the wasted teen who crashed into a young couple, killing the girl and permanently disabling the boy; the accidents, sexual assaults, and alcohol poisonings that are legion.

Under the social host law, a person who hosts an underage drinking party can face up to a year in prison and a fine of up to $2,000. Police thought they had a clear violation here. The mother volunteered that she had taken away the kids’ keys so they couldn’t drive, an apparent acknowledgment that she knew they were drinking, or were likely to.

And this wasn’t just any mother. This was Tracy A. Miner
, a well-regarded, well-connected attorney at a big Boston law firm. Ordinarily, the Plymouth County DA would handle this case, but Miner had contributed to his campaigns, so District Attorney Timothy Cruz asked the Bristol County DA to step in.

In Hingham District Court, the case landed before a clerk-magistrate with his own reputation: Joseph Ligotti, a mercurial, politically-wired official twice disciplined for inappropriate conduct and insensitivity. But he seemed to go out of his way to be sensitive to Miner. Despite pleas from police and the ­assistant district attorney, he refused to issue a complaint. Instead, he left the case open for six months, placing her on a kind of probation.

Almost always, say people who deal with this law, clerk-magistrates will issue complaints if police ask for them, and especially if prosecutors do.

But not Ligotti. If this was his idea of ­mercy, it was badly misplaced.

At the hearing, Miner said she didn’t know her guests were drinking, according to someone familiar with the proceedings. (Miner did not respond to requests for comment.) She said she went up to her room at 11:30 on New Year’s Eve, leaving her daughter with just a small group of girlfriends, and that dozens of other teens arrived after that. She said she took the keys away not because she knew they were drinking, but so they wouldn’t drive on a dangerous night. The hundreds of empty bottles police found in the house were, she claimed, from other parties.

None of this passes the smell test. But Ligotti gave Miner the benefit of the doubt. Sergeant Michael O’Hara, the Scituate police prosecutor, says the clerk-magistrate has done this before, blocking two other cases he tried to bring under the social host law.

Miner might not have fared as well elsewhere. In Essex County, where DA Jonathan Blodgett has made it a mission to hold parents responsible for underage drinking in their homes, Tiffany Clark
was sentenced to six months in prison in 2012, in a similar case. And in 2010, former Clinton selectman Mark Elworthy
was charged after teenagers got drunk at his home and a fight broke out — even though Elworthy said he wasn’t there at the time. A jury later ­acquitted him.

So what happened here? Is this the case of a person with outsize influence getting a break she wouldn’t get elsewhere? Or is it really true that kids can drink themselves senseless in a house where a parent is present, but completely clueless about what’s going on?

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